A polymer electrolyte fuel cell (hereinafter referred to as a “PEFC”) causes an electrochemical reaction between a hydrogen-containing fuel gas and an oxygen-containing oxidizing gas, such as air, to generate electric power and heat at the same time. A unit cell (cell) of the PEFC includes a MEA (Membrane-Electrode Assembly), gaskets, and electrically conductive plate-shaped separators. The MEA is constituted by a polymer electrolyte membrane and a pair of gas diffusion electrodes (an anode and a cathode).
Generally, the PEFC is formed by stacking a plurality of cells described above, providing end plates on both ends of the stacked cells, respectively, and fastening the end plates and the cells with fastening members. Therefore, high stress (fastening pressure) is applied to the vicinity of a portion of the polymer electrolyte membrane, the portion contacting an outer periphery of a catalyst layer of the gas diffusion electrode (the portion of the polymer electrolyte membrane is hereinafter referred to as an “outer peripheral contact portion of the polymer electrolyte membrane), the high stress being higher than stress applied to the other portion. By repeating start-up and stop operations of the PEFC, tensile stress and compressive stress are repeatedly applied to the polymer electrolyte membrane. Especially, these stresses are strongly applied to the outer peripheral contact portion of the polymer electrolyte membrane, and the problem is that damages, such as distortions or cracks, of the outer peripheral contact portion tend to occur.
To solve such a problem, a cell of a polymer electrolyte fuel cell is known, in which a reinforcing member is provided over the inside and outside of the peripheral edge of an oxygen electrode catalyst layer or a fuel electrode catalyst layer (see PTL 1, for example). FIG. 21 is a schematic diagram showing the schematic configuration of the cell of the polymer electrolyte fuel cell disclosed in PTL 1. In FIG. 21, a part of the polymer electrolyte fuel cell is omitted.
As shown in FIG. 21, in a cell 200 of the polymer electrolyte fuel cell disclosed in PTL 1, an elastically deformable reinforcing member 204 is provided over the inside and outside of the peripheral edge of an oxygen electrode catalyst layer 202C so as to be located on one side of the oxygen electrode catalyst layer 202C, the side being opposite to a side where a polymer membrane 201 exists, and an elastically deformable reinforcing member 205 is provided over the inside and outside of the peripheral edge of a fuel electrode catalyst layer 203C so as to be located on one side of the fuel electrode catalyst layer 203C, the side being opposite to a side where the polymer membrane 201 exists. PTL 1 describes that: the reinforcing members 204 and 205 elastically deform; therefore, even if the tensile stress and the compressive stress are repeatedly applied to the polymer membrane 201, the application of the stress to an oxygen electrode boundary membrane portion 201W and fuel electrode boundary membrane portion 201W of the polymer membrane 201 is suppressed; and on this account, the damages, such as distortions or cracks, of the oxygen electrode boundary membrane portion 201W and fuel electrode boundary membrane portion 201W of the polymer membrane 201 are prevented.